Spoke calcs?

stoobydale

Ok, got the gear coming, next task is calculating the spoke lengths. I have some Campag Mirage hubs 32 hole and some Mavic CXP33 rims. Has anyone made up this combo before and if so can you remember what spokes you used? I am going to try a 3 cross pattern.

dennisn

stoobydale wrote:

Ok, got the gear coming, next task is calculating the spoke lengths. I have some Campag Mirage hubs 32 hole and some Mavic CXP33 rims. Has anyone made up this combo before and if so can you remember what spokes you used? I am going to try a 3 cross pattern.

I don't mess with trying to figure spoke length. I buy the spokes I need at the local bike
bike shop. It's good for business, they usually have acess to a good spoke length
program, they can cut spokes to length if required, and they are glad to help. I also buy the nipples from them. You might save a dollar or two through mail order but I think it's a
damn good idea to be known as a somewhat regular customer at your local shop. They
can be very helpful with things you can't do. And a really good source of general
bicycle knowledge and hints.

Dennis Noward

robbarker

There's a good online calculator at dtswiss.com, or google for spocalc. You can afford to have spokes a gnat's tadger too long with CXP33s and I would add 2mm to the DT swiss figure - it makes initial tensioning with your nipple driver easier. You're probably looking at 294 for the front and non-drive side rear, 292 for the drive side rear.

stoobydale

How mugh tolerance is there with the online calculators. I have use 2 and got two different results although they are quite close. The other thing that I have been told is to round down.

Machine head calculator=
Front wheel 291.7mm
Rear D/S 288.5
Rear NDS 291.3

DT Swiss calculator
Front wheel 292mm
Rear D/S 290
Rear NDS 292

If I added 2mm the DT swiss calculation would be as you suggested Robbarker.

robbarker

What you don't want to do with a traditional rim is to get the spokes much too long, as the thread can poke out of the end of the nipple and could thenn stick through the rim tape and puncture the tube. Not good.

Equally, you don't want them so short that you can't use a nipple driver effectively to take up the initial slack - it's vital that every spoke is tightened the same amount and the nipple driver is the way you ensure this happens. Too much tension too soon means you are in the PITA game of nipple driving each nipple, then backing off two or three turns on each one to maintain evenness.

CXP33s have the eyelets some way inboard of where the rim tape lies, so you can afford to go a couple of mm too long safe in the knowledge that you won't risk the spokes sticking into the tube. Don't go too mad though, as you want a good portion of the spoke and nipple threads overlapping. 2mm over the DT figure will work well.

aracer

The trouble is if you go too long you can end up bottoming the nipple on the spoke threads meaning you can't tighten them any more. They normally do this when there's less than 2mm poking out of the top of the nipple. Therefore I always go shorter than the calculated length given this also doesn't allow for the fact the spokes will stretch a bit when under tension.

robbarker

Yes indeed - I've never managed to get that far before but I did try and reuse some 294s on a wheel for my pub bike that really needed 289s according to DT (although the hub dimensions had to be hand-measured) and the spoke threads just poked out of the nipples. I think another turn would have bottomed them out. Unfortunantley the rims I was using meant that the little bit of spoke thread sticking out was a puncture risk, so I bit the bullet and bought new spokes.

From the wheels I've built so far I've concluded that a tiny bit too long makes life easier than a tiny bit too short, but that you need to be within 2mm of spot on.

LangerDan

You'll need to round up (or down) the calculated size to the commercially available sizes in any case. At least for part of their ranges, DT Swiss do spokes in even-numbered mm increments, Sapim do odd-numbered intervals.

Oh, according my LBS yesterday, there is a big delay from the distributors in some spoke sizes.

robbarker

DT produce spokes in 1mm increments - at least for Competition which is what I prefer to build with. It may be that some places only stock even sizes to cut down on their stock committment.

stoobydale

Robbarker, it's not the first time i've heard that you should add 2mm to the DT swiss calculator, but why is it? If it's consistently 2mm out you think that they would change the programme. I have also just read recently that you should use 14mm nipples wit the CXP33 rims. Have you found this to be the case in your experience? I have also found a shop in europe where the spokes are cheaper even including the P&P, unbelievable, the prices we pay for things in the UK.

NervexProf

stoobydale wrote:

Robbarker, it's not the first time i've heard that you should add 2mm to the DT swiss calculator, but why is it? If it's consistently 2mm out you think that they would change the programme. I have also just read recently that you should use 14mm nipples wit the CXP33 rims. Have you found this to be the case in your experience? I have also found a shop in europe where the spokes are cheaper even including the P&P, unbelievable, the prices we pay for things in the UK.

Stooby - can you provide a link to the European website where spokes are cheaper...?

I think that UK suppliers 'rip us off' with spoke prices..and I use a lot of spokes, preferring to buy in boxes of 100, or a gross.

robbarker

I've just measured - 12mm nipples have about 6mm sticking out - enough to be useable. 14mm have about 8mm sticking out. I'd go with 14mm. If you use 14mm nipples then my spoke lengths would be 290 and 292 for your components.

Have you looked at ACI spokes at Velomax? They are very good value.

I have a sneaking feeling that DT make an allowance for spoke stretch in their calculator. The accepted equation is in Mussons book if you're interested.

If you're really interested, have a look at this:

http://www.bikephysics.com/wheel.pdf

If you are up to the maths, you will finally understand how bicycle wheels work!

LeighB

On the subject of wheel building can anyone tell me if the size of the flange on older Campag hubs is the same as the modern ones? I have small flange (approx 46mm) Campag front wheel that is about 15 years old and the cones and bearings are pitted but the Mavic rim is perfect. I have seen modern Campag hubs available for reasonable prices and wondered if I could do a ‘hub changeover’ with the same length (or even the original) spokes.

dennisn

LeighB wrote:

On the subject of wheel building can anyone tell me if the size of the flange on older Campag hubs is the same as the modern ones? I have small flange (approx 46mm) Campag front wheel that is about 15 years old and the cones and bearings are pitted but the Mavic rim is perfect. I have seen modern Campag hubs available for reasonable prices and wondered if I could do a ‘hub changeover’ with the same length (or even the original) spokes.

Because I go to the bike shop for spokes, nipples, rIms and let them tell me what I need,
I'm not sure how all of the online spoke calculators work. I simply tell the shop what
hubs, rims, and the lacing pattern I'm going to use, they go online to a service that they
actually pay to use or subscribe to. They punch in a few numbers and "bingo" spoke lengths pop out. They then cut the spokes to the length required if they don't have a specific size in the shop. I'm on my way with the right stuff and life is good. Don't believe
I wouldn't recommend reusing spokes old spokes. All things considered, it isn't that expensive to buy new.

Dennis Noward

stoobydale

Nervexprof, the european website is "starbike.com" since finding them I also found a UK shop called "sjscycles.co.uk" which were very good on price, but after taking advice from robbarkers post on the spoke sizes and nipples the LBS matched the price of sjs so that's where i'm getting them from.

Thanks for the advice rob, I have gone with your calculations, ie 2mm longer than the DT swiss online calculator. Like you said even if they are a bit too long there is no way they will poke out of the wells on these rims.

I thought that I had purchased a wheel jig from Probikekit but after 2 weeks of waiting they have told me that they can't supply it. Any recommendations for a cheap one?

NervexProf

stoobydale wrote:

Nervexprof, the european website is "starbike.com" since finding them I also found a UK shop called "sjscycles.co.uk" which were very good on price, but after taking advice from robbarkers post on the spoke sizes and nipples the LBS matched the price of sjs so that's where i'm getting them from.

Thanks for the advice rob, I have gone with your calculations, ie 2mm longer than the DT swiss online calculator. Like you said even if they are a bit too long there is no way they will poke out of the wells on these rims.

I thought that I had purchased a wheel jig from Probikekit but after 2 weeks of waiting they have told me that they can't supply it. Any recommendations for a cheap one?

Thanks for the info Stooby - I have sent you a pm re a wheel jig.